The present invention relates generally to a closed-ring transparent optical communication network that provides for the protection of the principal communication channel of each supported wavelength and for the management of low priority traffic.
A significant problem in optical fiber communications between various points is guaranteeing adequate protection against possible damage to the transmission means and/or part of the communication apparatus without resorting to elements external to the communication network, for example, centralized supervision, and that also permits contemporaneous maximum utilization of the transmission band. It is also necessary that a breakdown in communication between two nodes not cause a breakdown in communication between the other nodes of the network.
The prior art has attempted to deal with these problems in various ways. For example, EP 0 729 247 describes an optical fiber synchronous bidirectional ring network wherein each fiber of the ring handles two signals of different wavelengths. For example, a 1310 nm wavelength signal is used as an operating signal and a 1550 nm signal is used as a reserve signal. The network is constructed such that in fault free conditions the first wavelength can be used for exchanges between network elements, while at the same time the second wavelength can also be used to maximize transmission capacity. During a fault condition, the second wavelength is used.
In another example, EP 0 677 935 discloses a communication network that includes a number of stations, S1-S3, that are distributed around a closed optical loop 30 having two access nodes N1, N2 on a transmission line LT or arc of the main loop. The information from these two nodes is carried on different wavelengths. The loop also includes an emergency optical fiber 31 and is protected against the failure of either node. For data reception, a station chooses one of the two wavelengths on the normal loop, or the emergency loop if the other is broken.
EP 0,769,859 discloses a transparent optical self-healing ring communication network. The network consists of two optical communication lines coupled to at least two optical signal add/drop nodes. In the network at least one of the add/drop nodes can selectively drop optical signals from one of the lines and can also simultaneously input at least one optical signal into each of the lines.
The prior art, in particular ITU-T Recommendation G.803, addresses various protection schemes, and in particular Path Protection, Multiplex Section Protection (MSP), Multiplex Section Dedicated Protection Ring (MS-DPRING) and Multiplex Section Shared Protection Ring (MS-SPRING).
Path Protection is applied only to unidirectional rings and consists in duplicating transmission on the working and protection branch and having a switch only in the receiver. Thus, a single node effects protection and there is single-ended operation without APS (Automatic Protection Switch) protocol. Path protection is also defined as Sub-network connection protection.
Multiplex Section Protection (MSP) is based on failure detection at the multiplex section level. It is characterized by two or more parallel multiplex sections, one of which is used for protection. It has a dual-ended operation because it requires a communication between the two nodes at the ends of the breakdown for commutation on the protection line using the APS protocol.
Multiplex Section Dedicated Protection Rings (MS-DPRING) are unidirectional rings with 1+1 protection. Under a failure condition the entire stream of data is looped to the protection channel by the two nodes on each side of the failure. The operation of this type of ring class is always dual ended. At an SDH level, the APS protocol is required.
Multiplex Section Shared Protection Rings (MS-SPRING) are bidirectional rings in which half of the capacity of the internal and external ring is reserved for protection. This capacity can be shared by several links and thus the throughput of the network is increased. However, such a system can only be used for TDM multiplexing and not for WDM multiplexing.
Applicants have discovered the need for a WDM optical communication network in which the principal channel can be directed onto the occasional or reserve channel when there is a breakdown of or degradation in the principal channel, without having to transmit at a different wavelength, without central control and without the electro optical conversion of the communication channels.
Applicants have also found that an optical communication network can be configured such that under fault free conditions, 100% of the communication capacity can be utilized by transmitting and receiving priority signals through a first communication arc of the network at a particular wavelength and transmitting and receiving occasional traffic through a second arc of the communication network at the same wavelength.
Accordingly, the present invention can be used for communication between various sites, generally when a high transmission capacity is needed. Furthermore, the present invention provides a mechanism for the protection of priority communication in the case of damage or breakdown. Management of the occasional channel permits a 100% utilization of the transmission capacity for the entire duration of the operating time when there is absence of damage to the network. In the case of a breakdown of or degradation in the priority channel, the priority traffic is redirected to the occasional channel.
Accordingly, the present invention is directed to a method and apparatus for providing a transparent optical communication network with a two-fiber bidirectional ring with autoprotection and management of occasional traffic that substantially obviates one or more of the limitations and disadvantages of the above-described prior arrangements. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
To achieve these and other objects and advantages, and in accordance with the purpose of the invention as embodied and broadly described herein, the present invention comprises an optical communication network capable of carrying optical signals at a plurality of wavelengths bidirectionally, the network comprising an internal fiber optic link capable of carrying the plurality of wavelengths in a first direction; an external fiber optic link capable of carrying the plurality of wavelengths in a second direction that is opposite to the first direction; a first communication channel for at least a first wavelength in said plurality, comprising first portions of the internal and external fiber optic links, the first communication channel being terminated by two nodes; a second communication channel for said first wavelength, comprising second portions of the internal and external fiber optic links, the second communication channel being terminated by the two nodes; detection circuitry for determining degradation in the first communication channel; a plurality of optical switches activated by the detection circuitry for redirecting communications at said wavelength from the first communication channel to the second communication channel upon detection of degradation in the first communication channel.
In another aspect, the present invention is a method for correcting the failure of a fiber optic link in an optical communications network comprising providing at least two fiber optic links capable of carrying a plurality of wavelengths of light; forming from the fiber optic links at least two optic communication channels for at least a first wavelength among said plurality; detecting degradation of the quality of transmission in any of the optical channels; and actuating optical switches to switch the transmission of said first wavelength from the channel in which degradation is detected to another channel.